This is an exponential growth problem. Exponential growth can be expressed mathematically in the following way:

.
Parameter a presents initial amount.
Parameter r is percentage increase.
Parameter t is time.
An equation that would describe given problem is:

t is the time in years.
I attached the graph of this function.
In this problem there might be a number that you need to add before the "( x 3)" then your answer will be 20 = 32 - 12 = 20
First, we need to solve for the common ratio from the data given by using the equation.
a(n) = a(1) r^(n-1)
15 = -3 r^(2-1)
-5 = r
r = -5
Then, we can find the sum by the expression:
S(n) = a(1) ( 1 - r^n) / 1-r
S(8) = -3 (1 + 5^8) / 1+5
S(8) = -195313
Hi don’t know but have a wonderful day
When you subtract a negative, it changes it to adding a positive.
= -2.5 - (-3.25)
= -2.5 + 3.25
= 0.75
Hope This Helped! Good Luck!